Method for air-fuel ratio sensor diagnosis

Abstract

A method is disclosed for controlling operation of an engine coupled to an exhaust treatment catalyst. Under predetermined conditions, such as after an engine cold start, the method operates an engine with a first group of cylinders having a first ignition timing, and a second group of cylinders having a second ignition timing more retarded than the first group. In addition, the engine control method also provides the following features in combination with the above-described split air / lean mode: idle speed control, sensor diagnostics, air / fuel ratio control, adaptive learning, fuel vapor purging, catalyst temperature estimation, default operation, and exhaust gas and emission control device temperature control. In addition, the engine control method also can change to combusting all cylinders at substantially the same ignition timing under preselected operating conditions such as fuel vapor purging, manifold vacuum control, and purging of stored oxidants in an emission control device.

Description

1. Field of the InventionThe field of the invention relates generally to air-fuel ratio sensor diagnosis.2. Background of the InventionThere are various methods used for determining whether an exhaust air-fuel ratio sensor has been degraded. For example, one method is to look for switching during closed loop control around stoichiometry. If the sensor switching reduced, then degradation could be found. Another method is to determine whether the sensor is operating within predetermined range around a desired air / fuel ratio.The inventors herein have recognized a problem with prior approaches. In particular, when using a system in which the sensor is exposed to air pumped through a cylinder, the sensor may stop switching, or be forced beyond the predetermined range. Thus, even for a sensor that has not degraded, a false indication can be provided that the sensor is degraded.SUMMARY OF INVENTIONThe above disadvantages are overcome by a system, comprising: an engine having a first group ...

AI Technical Summary

Benefits of technology

By determining whether the sensor indicates lean when exposed to air pumped through a cylinder that is not combusting, it is possible to check functionality of the sensor and prevent false indications that the sensor has degraded.

In other words, if a large engine load is placed on the engine and adjustment of engine air flow and the first cylinder group ignition timing to the optimal ignition timing is insufficient to maintain the desired engine idle speed, then additional torque is supplied from the second cylinder group by advancing the ignition timing towards the optimal ignition timing. While this reduces the engine heat generated, it only happens for a short period of time to maintain engine idle speed, and therefore, has only a minimal effect on catalyst temperature. Thus, according to the present invention, it is possible to quickly produce a very large increase in engine output since the engine has significant amount of ignition timing retard between the first and second cylinder groups.

Problems solved by technology

If the sensor switching reduced, then degradation could be found.

In particular, when using a system in which the sensor is exposed to air pumped through a cylinder, the sensor may stop switching, or be forced beyond the predetermined range.

Thus, even for a sensor that has not degraded, a false indication can be provided that the sensor is degraded.

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